From the time of the ancient Roman triremes, man has sought improved mechanisms of locomotion across the Earth's great bodies of water. Indeed, the oarsman was perhaps the first in the long line of reciprocating marine propulsion engines, pulling his oar through the water to obtain a reactive propulsive force in one direction, and then returning the oar with a minimum of resistance in the water to the beginning position for the next stroke.
Since those ancient times, many attempts have been made to improve on the reciprocating marine propulsion engine. For example, U.S. Pat. No. 1,688,376 to Bidoire discloses a relatively complicated mechanism for obtaining locomotion through water by means of a reciprocating propeller. Bidoire describes a multiple trap-door arrangement which is pushed and pulled through the water by means of a plurality of reciprocating arms which extend through the hull of the vessel to be propelled. The trap-doors are mounted to a rectangular frame and close during the thrusting portion of the cycle while opening to pass water with less resistance during the return portion of the cycle. A substantial amount of frictional loss of energy is suffered by the Bidoire apparatus through the work required to push and pull the driving rods through the stuffing boxes in the hull of the ship, which must be kept water-tight. The outrigger suspension of the trap-door frame by the drive rods undergoes great stresses in operation, which requires the use of large structural members to maintain the close dimensional tolerances required in the Bidoire design. In addition, the Bidoire device has a rectangular cross section which requires extensive machining to fabricate, making it an expensive assembly. The combination of low energy efficiency, excessive bulk and difficulty in fabrication have contributed to the inability of prior art reciprocating marine engines such as that of Bidoire's to successfully compete with other marine propulsion technologies.